The first prototype, UB-14, was destroyed in a 1935 accident attributed to faulty maintenance on the aileron control system. Burnelli then designed and built an improved version, the UB-14B. A modified version of the UB-14B design was built under licence in the United Kingdom by Cunliffe-Owen Aircraft, powered by two Bristol Perseus XIVC radials as the Cunliffe-Owen OA-1. This design was to have had streamline inline engines. The OA-1 used radial engines.
In September 1936, Burnelli applied to the CAA for approval to fly a transatlantic flight with Clyde Edward Pangborn as the selected pilot. The Cunliffe-Owen failed its airworthiness certification due to excessive takeoff run and poor workmanship. It was performance tested at the A&AEE Boscombe Down in 1939. After appropriate work, in June 1941 Jim Mollison and an Air Transport Auxiliary crew delivered Cunliffe-Owen OA-1 G-AFMB to Fort Lamy, Chad. The aircraft was fitted out as a personal transport for General De Gaulle. It was later abandoned at Kabrit, and burned during VJ-Day celebrations. The other one aircraft landed in Vichy France en route to Fort Lamy